Study on Steep Front Impulse Test Voltage Value of Disc Insulators with Variation in the Number of Units of Insulator String

The insulators used in power transmission and distribution networks should withstand abnormal system-generated switching impulses and natural lightning impulses. To avoid the failure of insulators in the field, the impulse puncture strength evaluation of the ceramic insulators is important. IEC 61211 standard stipulates the procedure to evaluate the ceramic disc insulators’ strength to withstand steep front impulses. In this test, the test voltage is determined by using a short standard string of five insulators. This paper presents the variation in the impulse stresses across the disc insulator units in the string due to non-linear voltage distribution under impulse flashover. This paper also correlates the test voltage values defined by the IEC standard with the highest stress on insulator units under impulse flashover of string insulators by using voltage distribution. The correlation study has been carried out with insulator strings having different arcing distances by using a different number of units.